Field of the Invention
The present invention relates to a die cushion device, and more particularly, to an inexpensive and functionally efficient die cushion device.
Description of the Related Art
Heretofore, there is proposed a die cushion device configured to create die cushion pressure by using a balance piston type relief valve (Japanese Patent Application Laid-Open No. 2001-079694, hereinafter referred to as PTL 1).
The die cushion device described in PTL 1 includes, as a device that creates hydraulic pressure to be supplied to a cushion cylinder, a first hydraulic creation mechanism that creates low hydraulic pressure, and a second hydraulic creation mechanism that creates high hydraulic pressure. In the die cushion device, the first hydraulic creation mechanism first applies low hydraulic pressure to a cushion cylinder after molding for each molding cycle to extend the cushion cylinder, and while the cushion cylinder is positioned near a top dead center, the second hydraulic creation mechanism applies high hydraulic pressure to the cushion cylinder to increase the cushion pressure in advance. In addition, when die cushion is operated, hydraulic oil in the cushion cylinder is returned to a sealed oil tank through a pilot check valve to which pilot pressure (high hydraulic pressure) is applied and a pilot relief valve to which compressed air is applied.
Here, the first hydraulic creation mechanism is composed of the sealed oil tank, a compressed air supply source that supplies compressed air at low pressure to the sealed oil tank, and the like, and the second hydraulic creation mechanism is composed of a hydraulic pump and an electric motor, which are continuously operated during operation of a press machine.